The present invention relates to a method and apparatus for allocation of a frequency band within a given frequency spectrum of a telecommunications system, as well as the telecommunications network itself The present invention may also relate to a control element for transceiver such as a base station, a base station controller or a mobile station in a radio telecommunications system capable of carrying out the method in accordance with the present invention. The invention is particularly suited to a telecommunications system which includes at least one radio system, particularly a mobile radio system using spread spectrum techniques or a combination of spread and non-spread techniques.
FIG. 1 is a schematic representation of a telecommunications system 100 which A includes a network 104 which may be a wireline telephone and/or data network. Network 104 may be connected via service node 103 to further networks 101 and 102 which may be synchronous (STM) or asynchronous (ATM), wireline or wireless networks. The network 104 may be connected to radio telecommunications transceivers 106-1, 106-2, 106-3, 106-4 via access nodes 105-1, 105-2, 105-3. The transceivers 106 may be part of the telecommunications network 104 or may be part of separate cellular mobile telephone or public radio system or systems. Further, the network 104 may be connected via a transceiver 109 to a satellite system including at least one satellite 110. The foot-print of the beam from the satellite 110 may overlap with the radio coverage of the transceivers 106. The network 104 may also be connected to a telecommunications system in building 111 which may form a micro- or picocellular radio telecommunications system within a macrocellular telecommunications system served by one or more of the transceivers 106 and/or satellite 110. Alternatively, building 111 may contain a cordless telephone system connected to network 104 by a wireline. Mobile stations 108 may be able to receive and transmit messages via any of the transceivers 106 and 109 and satellite 110 including communication via the cordless or wireless network within building 111. In addition the building 107 which may be a private house may be connected to network 104 by a so-called wireless local loop (fixed wireless access), i.e. a part of the connection to building 111 is via a radio link.
In addition to the above telecommunications systems there may also be other sources of radio noise, e.g. point-to-point microwave communication systems, CB radio, military communications systems. The result is a considerable amount of radio activity within a certain, normally allocated or regulated frequency spectrum. Conventional approaches to preventing interference between the types of radio system mentioned above require the allocation of fixed frequency bands as exemplified by the conventional systems described in U.S. Pat. Nos. 5,452,471, 5,428,819 or EP 0 719 062 for instance.
When all the telecommunications systems mentioned above are operating, there are a plurality of existing transmissions as indicated schematically in FIG. 2a. Within a frequency spectrum S between the lower and higher frequency limits fo and fe various radio telecommunications transmissions occupy part of the spectrum, e.g. wideband communications W, narrow band communications N, a point-to-point microwave communications transmission O. At any arbitrary location within the geographical coverage area served by all the systems at which a transmission is to be initiated these signals, each one of which is a function of power and frequency, combine as shown schematically in FIG. 2b. The resulting cumulative power/frequency diagram will be called a xe2x80x9cpower spectrumxe2x80x9d in accordance with the present invention whereas xe2x80x9cfrequency spectrumxe2x80x9d will be used to refer to the range of frequencies which can be used for communications within a telecommunications system.
Parts of the generalised communications systems of FIG. 1 may have fixed and protected frequency bands, e.g. the microwave system O, or emergency, hospital or police communications transmissions which may be wideband, broadband or narrowband. Narrowband in accordance with the present invention means a communication which requires relatively little bandwidth because the amount of information to be transmitted is small. Wideband in accordance with the present invention means a communication which has a significantly wider bandwidth than required for the information to be carried. Broadband in accordance with the present invention means a communication which requires a broad bandwidth due to the amount of information to be transmitted. In accordance with conventional methods, any new telecommunications system is allocated a fixed bandwidth in a remaining part of the frequency spectrum S in such a way as to avoid interference between the systems, i.e. usually by providing a frequency guard gap between the new system and any existing system. One disadvantage of such conventional allocation methods is that frequency spectrum may be left unused or may be inefficiently used, i.e. the spectral efficiency is low unless every system is used heavily.
So-called etiquette regulations are known for unlicensed bands of radio frequency for use by mobile radio, e.g. telephone or data services as described for instance in the article xe2x80x9cCoexistence and Access Etiquette in the United States Unlicensed PCS Bandxe2x80x9d, by Steer, IEEE Personal Communications Magazine, fourth quarter 1994. The main etiquette rules described in this article are:
1) the co-ordination rulexe2x80x94every communication between a fixed station (sometimes called a port) and a mobile station must start from a fixed station. A mobile station xe2x80x9clistensxe2x80x9d for a marker or beacon signal from a fixed station and requests access thereto before a communication may be initiated from a mobile station.
2) The listen before transmit (LBT) rulexe2x80x94before the fixed station transmits a marker or beacon signal it first measures the interference in the time/frequency window in which it intends to transmit.
3) The 30-second rulexe2x80x94a marker or beacon signal may only be transmitted for 30 seconds maximum without acknowledgement from another station wishing to transmit to it and periodic acknowledgements must be received every 30 seconds.
4) The packing rulexe2x80x94the LBT must be carried out so that frequencies are either scanned in increasing or decreasing order and the first acceptable frequency must be taken. Transmissions having a bandwidth below a first limit, e.g. below 625 kHz, scan from the lower frequency limit upwards and transmissions having a second bandwidth, e.g. above 625 kHz, scan from the upper frequency limit downwards. This rule packs the wider bandwidth communications in the upper part of the frequency spectrum and the narrower bandwidth communications in the lower part of the frequency spectrum.
5) The power level rule, the power level of a communication is limited by its bandwidth.
One application of such rules is described in the article xe2x80x9cOn channel definitions and rules for continuous dynamic channel selection in coexistence etiquettes for radio systemsxe2x80x9d, by D. Akerberg, 44th IEEE Technology conference Stockholm, June 1994, pp. 809-13. In this scheme a system access channel is described as free, i.e. available for transmission, if the power at a particular frequency as determined during LBT is less than the thermal noise floor plus 24 dB. If no free channel is available then a least interfered channel (LIC) is selected if the result of the LBT is a frequency having a power level of less than the thermal noise floor plus 60 dB. It is stated that such an etiquette regulation is not suitable for use with frequency hopping code division multiple access (FH-CDMA) or Direct sequence code division multiple access schemes (DS-CDMA). One reason for this is that DS-CDMA suffers from the xe2x80x9cnear-far problemxe2x80x9d and this is normally solved by power control particularly on handover. The power rules mentioned above are too crude to allow for such a power control.
Spread spectrum techniques are known to the skilled person and include fast :frequency hopping and direct sequence techniques. Spread spectrum communications may be defined as systems that possess the two characteristics: 1) the transmitted signal is spread over a frequency band wider than the minimum bandwidth required for the information to be sent, and 2) the spreading of the signal is achieved by encoding it with a pseudo-random code sequence, sometimes known as pseudo-noise (PN) which is independent of the information itself. In the receiver a despreading operation must be carried out to extract the original data signal.
Summaries of these techniques may be found in the articles: xe2x80x9cSpread Spectrum Communication Techniquesxe2x80x9d, by Tsui and Clarkson, Electronics and Communication Eng. Journal, vol. 6, number 1, February 1994, pp 3-12, and xe2x80x9cSimplified matched filter receiver designs for spread spectrum communications applicationsxe2x80x9d, by Povey and Grant, Electronics and Communication Eng. Journal, vol. 5, number 2, April 1993, pp 59-64 and xe2x80x9cPseudo noise sequences for engineersxe2x80x9d, by Mutagi, Electronics and Communication Eng. Journal, vol. 8, number 2, April, 1996, pp 79-87. It is known to use such techniques with frequency division and also with combined frequency and time division multiple access.
An object of the present invention is to organise a plurality of telecommunication systems operating within a frequency spectrum, each free to place a communication within any non-excluded part of the spectrum, while reducing the conflict between the systems.
A further object is to provide coexistence of telecommunications systems in which at least one system uses spread spectrum techniques such as DS-CDMA.
A further object of the present invention is to provide a method of placing a next communication with a bandwidth xe2x80x9cBxe2x80x9d and power level xe2x80x9csxe2x80x9d at an appropriate place within a spectrum S in a radio telecommunications system so as not to cause serious interference to other users as well as not to be significantly interfered with by other users without having to rely on techniques which allocate specific frequency bands to specific communications.
The present invention includes a method of allocating a transmission centre frequency for a candidate transmission within a given frequency spectrum available for communications within a telecommunications system, the candidate transmission having a power/frequency characteristic representative of the power of the candidate transmission as a function of frequency, comprising the steps of providing a power spectrum representative of the cumulative effect of the power/frequency characteristics of at least a portion of the existing transmissions at a plurality of centre frequencies within the frequency spectrum at the time of allocation; evaluating allocation decision values defined by a first function of the power spectrum and the power/frequency characteristic of the candidate transmission; and selecting a centre frequency for the candidate transmission from the frequency spectrum based on a minimum value among the evaluated allocation decision values or based on an evaluated allocation decision value being below a first threshold value.
The present invention also includes a telecommunications system operating within a frequency spectrum available for communications, comprising: means for allocating a centre frequency for a candidate transmission, the candidate transmission having a power/frequency characteristic representative of the power of the candidate transmission as a function of frequency; means for providing a power spectrum representative of the cumulative effect of the power/frequency characteristics of at least a portion of the existing transmissions at a plurality of centre frequencies at the time of allocation; and the allocating means including: means for evaluating allocation decision values defined by a first function of the power spectrum and the power/frequency characteristic of the candidate transmission; and means for selecting a centre frequency for the candidate transmission from the frequency spectrum based on a minimum value among the evaluated allocation decision values or based on an evaluated allocation decision value being below a first threshold value.
The present invention also includes a frequency allocating device for use in a telecommunications system operating within a frequency spectrum, the frequency allocating device comprising: means for allocating a centre frequency for a candidate transmission, the candidate transmission having a power/frequency characteristic representative of the power of the candidate transmission as a function of frequency; means for providing a power spectrum representative of the cumulative effect of the power/frequency characteristics of at least a portion of the existing transmissions within the frequency spectrum at a plurality of centre frequencies at the time of allocation; and the allocating means including: means for evaluating allocation decision values defined by a first function of the power spectrum and the power/frequency characteristic of the candidate transmission; and means for selecting a centre frequency for the candidate transmission from the frequency spectrum based on a minimum value among the evaluated allocation decision values or based on an evaluated allocation decision value being below a first threshold value.
The present invention also includes a method of operating a frequency allocation device for allocating a transmission centre frequency for a candidate transmission within a given frequency spectrum available for communications within a telecommunications system, the candidate transmission having a power/frequency characteristic representative of the power of the candidate transmission as a function of frequency; comprising the steps of providing a power spectrum representative of the cumulative effect of the power/frequency characteristics of at least a portion of the existing transmissions at a plurality of centre frequencies within the frequency spectrum at the time of allocation; evaluating allocation decision values defined by a first function of the power spectrum and the power/frequency characteristic of the candidate transmission; and selecting a centre frequency for the candidate transmission from the frequency spectrum based on a minimum value among the evaluated allocation decision values or based on an evaluated allocation decision value being below a first threshold value.
In accordance with the present invention spectral efficiency may be improved by allocating bandwidth on a communication-by-communication basis within any regions of the spectrum S of FIG. 2 which are not specifically excluded or protected. For ease of calculation it is preferred if the power/frequency characteristic of the candidate transmission or the existing transmissions is a representative power level value and bandwidth value. The first function is preferably indicative of the interference of the existing transmissions on the candidate transmision, e.g. a multiplication or an integral function. Preferably, the selection of a suitable centre frequency is only carried out if the value of a second function of the power spectrum and the power/frequency characteristic of the candidate transmission is below a predetermined value. The second function is preferably indicative of interference of the candidate transmission on the existing transmissions, e.g. a multiplication function.
The dependent claims define further individual embodiments of the present invention. The present invention will be described with reference to the following drawings.